In the related art, a charge accumulation type imaging device (hereinafter, referred to as an accumulation type imaging device) as an imaging device with which an electronic apparatus having an imaging function represented by a digital camera is equipped is known.
In the accumulation type imaging device, when excessive light is incident and an accumulation charge amount exceeds a saturation charge amount, an excess portion of a signal charge flows into an N-type substrate beyond an overflow barrier or flows into a floating diffusion beyond a potential barrier under a transfer gate. Therefore, since a dynamic range of the accumulation type imaging device is limited by the saturation charge amount of a charge accumulation region, it is difficult to realize a large dynamic range and, as a result, there is a problem that overexposure or underexposure is likely to occur.
Thus, as a solid-state imaging device capable of solving such a problem, a logarithmic sensor configured of photovoltaic type pixels is proposed (for example, see PTL 1 or PTL 2).
FIG. 1 illustrates an equivalent circuit for one pixel of the photovoltaic type pixel configuring the logarithmic sensor disclosed in PTL 1.
In a photovoltaic type pixel 1, photovoltaic power proportional to a logarithm of a photocurrent value depending on incident light 2 is generated by a PN junction diode 3, the photovoltaic power that is generated is amplified by an amplifier 4 and becomes an image signal, and the image signal that is generated is output to a vertical signal line 7 through a switch 6. Moreover, the PN junction diode 3 is reset by a switch 5.
As described above, in the photovoltaic type pixel 1, since the image signal that is generated is output to a subsequent stage without being accumulated, even when excessive incident light 2 is incident, the pixel signal is not saturated.
Moreover, the photovoltaic type pixel 1 can be operated as an accumulation type.